Greenhouse gas emissions from sandy soils amended with lime and gypsum under different initial soil pH and nitrogen sources

Lime (CaCO3) application has led to an inconsistent mitigation of greenhouse gas emissions (GHGs) from agricultural soils. In addition, only a few studies have investigated the impact of gypsum (CaSO4) on the release of GHGs. Therefore, here we investigated the impact of initial soil pH and nitrogen sources on CaSO4 and CaCO3 effectiveness in reducing the production of GHGs. We hypothesized that (i) liming presents the highest effectiveness in reducing GHGs when performed in acidic soil and under NO3--N fertilizer application, and (ii) application of CaSO4 is not effective in reducing GHG irrespective of the initial soil pH or nitrogen (N) source. Firstly, an incubation experiment was carried out to evaluate the effect of initial soil pH using acidic soil and neutral soil amended with CaSO4 and CaCO3. Subsequently, a second incubation experiment was conducted to investigate the effect of N source by applying calcium nitrate and urea in an acidic soil amended with CaSO4, CaCO3 and CaSO4 + CaCO3. The measured variables were soil pHH(2)O, daily and cumulative emissions of N2O-N, CO2-C and CH4-C, as well as NH4+-N and NO3--N concentrations. CaCO3 did not affect N2O-N emission under neutral soil pH, and NO3--N fertilizer application. However, CaCO3 increased N2O-N release under acidic soil (+96%), and urea fertilizer application (+97%). Furthermore, CaCO3 and CaSO4 reduced CO2-C emission from the neutral pH soil by 31%, and CaSO4 decreased the mean cumulative N2O-N release from the soil fertilized with urea-N by 43%. In conclusion, this study did not confirm liming as an alternative to reduce N2O-N release under different initial soil pH and N sources. Furthermore, our results indicated that CaSO4 may decrease GHG emissions. Finally, these results suggest caution for considering liming as a strategy to mitigate N2O-N emission from agriculture.